<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>稀疏数组</title>
</head>

<body>
  <script>
    let a = new Array(3)
    a = []
    a[3] = 0
    console.log(a);

    let b = [, , null]
    console.log(b);
    console.log(b[0]);
    console.log(b[2]);
    console.log(b[0] == b[1]);
  </script>
</body>

</html>